This invention relates to apparatus and methods for measuring the radial runout of rotating objects. More specifically, the invention relates to apparatus and methods for measuring the radial runout, or circumferential out-of-roundness deviation of a shaft.
Conventional methods of inspecting and measuring the runout of shafts and other such similar parts require the use of precision supports for rotation of either the inspection part or the measurement gauge to establish the parts center or a reference surface. Setup and use of these devices generally requires the labor of several highly trained and skilled technicians. The inspection operation can be very time consuming, labor intensive, expensive and tedious to perform. In some cases, it is extremely difficult to utilize current methods of inspection. This is especially true for large rotating objects, such as generator rotors and turbine assemblies.
Conventional shaft runout measurement techniques typically require the presence of at least two operators. First, the surface of the shaft is prepared by cleaning and ensuring that there are no raised edges which might harm a contact-type gauge. Eight points are then marked around the circumference of the rotor coupling at evenly-spaced intervals of forty-five degrees. The shaft is supported at each end in a precision center, such as a lathe, and is rotated for a predetermined period of time to eliminate weight-induced bowing. As the shaft continues to rotate slowly, one operator positioned near the rotor coupling signals the other operator when each point passes a fixed reference point, the other operator reads the measured runout at five runout points and manually records the measurements. The five runout points include one point on each journal, one point on each coupling and one point intermediate the journals/couplings. All runout measurements are recorded as positive numbers, as only the total indicator runout (TIR) is of interest. On average, the runout measurement operation is performed fifteen times on different sections along the axial length of the rotor. If appropriate, axial runout measurements and shaft float measurements are also taken, axial runout points are adjusted using acceptance tolerances to reflect the actual axial runout, and the values of such measurements are manually recorded. The data collected during the measurement of the runout are then entered into a computer program, such as a spreadsheet, which solves for the Cartesian formula and the runout is manually plotted. After review and approval, the hard-copy runout report is generally stored for archival purposes. When this method is utilized, Runout measurements must be taken each time the machining setup is changed and is generally redone at each shift change to ensure proper setup of the shaft.
As may be easily appreciated, such conventional apparatus and method is man-power intensive and is therefore relatively expensive. Further, the measurement data is handled by personnel four separate times, allowing extensive opportunity for the introduction of error. In addition, the recorded data and the runout plots must be converted to an electronic format if they are to be archived in such form.
Briefly stated, the invention in a preferred form is a system and methods for measuring the radial runout, or circumferential out-of-roundness deviation of a shaft rotatably supported on a standard rest. The shaft includes a coupling, first and second journal surfaces.
The shaft runout measurement system comprises multiple surface sensing assemblies, including at least a first journal surface sensing assembly, a second journal surface sensing assembly, and a test surface sensing assembly which sense the first journal surface, the second journal surface, and a test portion of the outer surface of the shaft, respectively. Each of the surface sensing assemblies has a surface sensor and a transmitter in electrical communication with the surface sensor. The surface sensors continuously sense the radial position of the associated surface of the shaft. During rotation of the shaft, a transmitter of each surface sensing assembly transmits a runout signal proportional to the runout of the associated surface. Each of the runout signals is received by a receiver of a computer. A test operating system, stored in the memory of the computer, applies a normalization program, also stored in the memory, to compute normalized runout data by adjusting the runout signal from the test surface sensing assembly with the runout signals from the first and second journal surface sensing assemblies to factor out deflection of the shaft caused by the standard rest. The test operating system inserts the normalized runout data into predetermined data cells of a runout spreadsheet stored in the memory. Formulas and instructions stored in operator cells of the runout spreadsheet compute and plot the shaft runout.
The system may also comprise a magnetic field sensing device and a plurality of magnets. The magnets are mounted at radially spaced positions on the shaft coupling. A magnetic field sensor of the magnetic field sensing device is positioned proximate to the shaft. A transmitter in electrical communication with the magnetic field sensor transmits an initiation signal each time a one of the magnets passes the magnetic field sensor. In this system, each of the surface sensing assemblies also includes a receiver and the computer also includes a transmitter. The test operating system causes the computer transmitter to transmit a data request signal each time the computer receiver receives a one of the initiation signals and the transmitter of each surface sensing assembly transmitting a discrete runout signal on receipt of a data request signal by the receiver of the surface sensing assembly.
A method for measuring the runout of the shaft described above comprises the steps of attaching the magnets at radially equidistantly spaced points on the shaft coupling. The magnetic field sensor of the magnetic field sensing device is positioned proximate to the shaft coupling such that the magnets are rotatable through a sensing field of the magnetic field sensor with out contacting the magnetic field sensor. The surface sensors of the first and second journal surface sensing assemblies are positioned for sensing the first and second journal surfaces of the shaft, respectively, and the surface sensor of the test surface sensing assembly is positioned for sensing the test surface portion of the shaft. The shaft is rotated, with the surface sensing assemblies continuously sensing the radial position of the associated surface of the shaft and a test run is initiated. Each time a one of the magnets rotates past the magnetic field sensor, an initiation signal is transmitted from the transmitter of the magnetic field sensing device. Each time the transceiver of the computer receives an initiation signal, the computer transmits a data request signal. Each time the transceiver of the surface sensing assembly receives a data request signal, it transmits a discrete runout signal. The computer receives the discrete runout signals and normalizes the runout signal from the test surface sensing assembly to factor out deflection of the shaft caused by the standard rest. The normalized runout signals are then inserted into predetermined data cells of a runout spreadsheet stored in memory of the computer and the runout spreadsheet computes and plots the runout.
It is an object of the invention to provide more efficient systems and methods for measuring the runout of a shaft.
It is also an object of the invention to provide systems and methods for measuring the runout of a shaft which require less operator action and input and are therefore less prone to error.
Other objects and advantages of the invention will become apparent from the drawings and specification.